Typically, a conventional diesel engine has one needle valve and one spring, wherein the needle valve is opened when fuel having pressure higher than opening pressure is introduced and is closed when the fuel has lower pressure.
In this manner, when fuel of high pressure formed in a fuel pump enters to a fuel valve, if the pressure higher than the opening pressure is formed within the fuel valve, through pressure of fuel oil, the spring lifts the needle valve against a force pressing against the needle valve, such that fuel is injected into a cylinder through multiple nozzle holes located on an end terminal of a nozzle. Such a method consists of one mechanism in which all nozzle holes are opened according to a predefined one opening pressure, and thus, after the opening pressure is formed, even if higher pressure is introduced to the fuel valve, injection should be continued only through a predefined number of nozzle holes. Therefore, when an operation of an engine at low speed or low load continues, the injection does not occur and, with respect to the pressure higher than the opening pressure, the injection occurs through all nozzle holes regardless of a level of pressure such that an injection pattern is not proportional to pressure and an injection amount cannot be adaptively controlled based on pressure. Also, since multiple fabricated nozzle holes open or close at the same time, residue fuel remaining between the closed needle valve and the nozzle after the injection is finished flows into the cylinder through the nozzle hole, thereby causing a problem related to exhaust gas and fuel economy.
Referring to FIG. 15, a Wartsila-Sulzer approach, an MAN-B & W approach, and a medium-size engine, which are a representative form of a conventional fuel valve, are described. In the Wartsila-Sulzer approach, when pressure is greater than the opening pressure but fails to form a high pressure, fuel flows into the cylinder rather than being injected into the cylinder through multiple nozzle holes fabricated on the nozzle. Also, even after the fuel injection is finished, a space (SAC volume) between the closed needle valve and the nozzle hole is large such that residue fuel remaining in this space flows into the cylinder, thereby causing the problem of harmful gas as described above. In the MAN-B & W approach, a needle valve in a slide method is adopted to reduce the SAC volume, however, the MAN-B & W approach has limitation in that the pressure beyond the opening pressure may not be actively coped with. In other words, although the SAC volume is fixed, according to the present invention, the SAC volume, which is a space between the low-pressure needle valve and nozzle, can be minimized after the injection is finished.
As shown in FIG. 15, in order for the needle valve to open at a predetermined pressure, a spring pressure is increased and fuel pressure is artificially increased in an apparatus other than the fuel valve to adjust the opening pressure; however, in the present invention, pressure is increased within the fuel valve such that fuel may be injected at high pressure even at low load.
In the conventional technology of FIG. 15, an injection timing is not determined by the fuel valve itself and the fuel previously introduced is injected at a predetermined pressure. In other words, the injection timing and maximum pressure of fuel oil is adjusted at a timing of introducing the fuel through fuel pump or other medium. In this regard, the present invention is configured to adjust the fuel injection timing by the fuel valve itself to adjust a time period to be prior to/subsequent to formation of the high pressure, thereby reducing harmful gas through optimum combustion.